> with a big enough lip/flange Your flange is not "big enough". For an absurd example, consider a hole 3" to a side, and a flange 48' in width. That said, I

> with a big enough lip/flange Your flange is not "big enough". For an absurd example, consider a hole 3" to a side, and a flange 48' in width. That said, I honestly meant this as a mathematical/rhetorical statement, not a practical one. So yes, you're correct that for any reasonable flange width (given the assumption we're talking about steel/iron manhole covers, and accepted values of the material's strength, etc.), some shapes wouldn't qualify. My point was to show that the question, taken at its face value, isn't even a good question. It assumes a flange, or no shape would work as a cover, as the cover would simply fall into its own hole. Thus, if we're to assume a flange (or a taper; it could be argued wine bottle stoppers and the holes they "cover" are both "circles"), we should be able to assume one of arbitrarily large size, and then ANY shape will work.